1. Field of the Invention
The present invention relates to an IR-ray absorptive compound and an optical recording medium utilizing the same.
In particular, the present invention pertains to an IR-ray absorptive compound and an optical recording medium with improved durability as evidenced by repeated information reproduction and light resistance. The present invention can be utilized in optical discs or optical cards.
2. Related Background Art
Generally speaking, optical recording media, for instance, an optical disc or an optical card record high density information by forming optically detectable small pits of, for example, 1 .mu.m on a thin recording layer provided on a substrate having a spiral, circular or linear groove thereon.
By scanning a laser beam which converges on the surface of the recording layer, the recording layer absorbs the laser energy and forms optically detectable pits, whereby information is written.
According to a heat mode recording system, the recording layer absorbs heat energy and forms a small pit (a concave portion) by evaporation or melting at that site. By using an organic dye thin film as the recording layer having high reflectance, the optical contrast of the recording pit can be set at a high level. For example, when a polymethine type dye, azulene type dye, cyanine type or pyrylium type dye, etc. with great light absorption relative to laser beam is used for an organic dye thin film, a light absorptive reflective film exhibiting metallic luster (i.e., reflectance on the order of 10 to 50%) can be obtained, providing an optical recording medium capable of laser recording and reflective reading. Particularly, when semiconductor laser with an oscillation wave length of 600 to 800 nm is used as the laser light source, there are further advantages in that the device can be made even smaller in size and lower in cost. However, organic dye thin films had the problems that recording and reproduction characteristics and storage stability may be lowered, because they deteriorate generally by the action of heat and light, etc.
To cope with such problems, U.S. Pat. No. 4,656,121 proposed a method to improve light resistance by incorporating an aminium salt or diimonium salt of a triarylamine type compound incorporated in a polymethine type dye.